text:
How does climb-rate vary with density/pressure altitude?
I'm seeking to write a little web or phone app which can help me choose the best cruising altitude based upon winds aloft. I know Garmin Pilot (and probably Foreflight) have a cruising altitude selector, but they don't seem to take into account the extra time/fuel required to get to the higher altitudes. I'm looking to make a calculator which factors that in.
I realize that the actual formulae for climb-rate, take-off distance, landing distance, etc are quite complex, but I don't need to generate them from scratch. What I plan to do is start with the charts in the performance section of the POH for a particular aircraft...

...and find some known values for climb-rate for given pressures/temps/weights and use curve-fitting to come up with simple formulae which are still within a few percent of what I would get with these charts.
Of course, to be as accurate as possible, it would be better to know, roughly, how climb-rate varies with pressure-altitude, density-altitude, weight, etc. Some of the adjustments (eg. for weight) seem to be fairly linear (at least over the domain of values of interest to us), while some others seem to have some curve... so maybe they vary as $b^{-x}$, $\frac{1}{x}$, $x^2$, $log(x)$...?
Does anybody know the general way in which climb-rate varies with these factors? (Bonus round: can you do the same for take-off and landing distances, in case I wanted to make a calculator for those?)

For propeller aircraft, the climb rate is a function of

available power
demanded power
weight
air density
wing lift

Five variables, and wing lift is itself a function of Mach number, Reynolds number, wing AoA, wing area. Available power is a function of air density, throttle setting, propeller incidence - demanded power a function of air speed, air density, angle of attack, Mach & Reynolds numbers. So in total a very large matrix of independent variables - in order to find equations via an analysis, we'll have to make some assumptions and simplifications. For instance that the aircraft thrust vector stays reasonably horizontal so that $T \cdot sin(\Gamma)$ is close to zero and can be disregarded. Also, that lift = weight during the climb.
For the steady climb, the weight equation then becomes $$W = C_L \cdot \frac{1}{2} \rho V^2 \cdot S \Rightarrow V = \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{1}{C_L}} \tag{1}$$
For the drag in horizontal flight:
$$ D_h = C_D \cdot \frac{1}{2}\rho V^2 \cdot S = \frac{C_D}{C_L} \cdot W \tag{2}$$
and the required power in horizontal flight $(P_r)_h$ becomes:
$$ (P_r)_h = D_h \cdot V = W \cdot \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} \tag{3}$$
The power required to maintain climb speed $C$ is $W \cdot C$ and available power $P_a = (P_r)_h + W \cdot C$, hence:
$$ C = \frac{P_a - (P_r)_h}{W} = \frac{P_C}{W} \tag{4}$$
Combine (3) and (4):
$$ C = \frac{P_a - (P_r)_h}{W} = \frac{P_a}{W} - \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} = \frac{\eta \cdot P_{br}}{W} - \sqrt{\frac{W}{S}\cdot\frac{2}{\rho} \cdot \frac{{C_D}^2}{{C_L}^3}} \tag{5}$$

Above picture shows a graph of $P_{br}$ of the P&W Wasp: function of manifold pressure and altitude. This engine had a turbo-charger for improved altitude performance, the engines of GA aircraft may not have these. Plots of variable pitch propellers show a propeller efficiency $\eta$ of about 0.8.
How this ties into the graph shown in OP:

The equations feature air density $\rho$. This is a function of static pressure and of temperature: an equation to convert to static pressure and vice versa can be found here.
Available power for a normally aspirated piston engine decreases as a function of altitude, approximately according to $\frac{({P_{br}})_h}{({P_{br}})_o} = (1 + c) \frac{\rho_h}{\rho_o}$. Tests on some American piston engines showed that for many of them a value of $C$ = 0.132 would be appropriate, refer to figure below which also shows the altitude-power function of a piston engine with supercharger.

All references and pictures from a university lecture book, paper copy only.

The climb rate depends on the excess power which is available after drag has been subtracted from net thrust. If the airplane stays at the same polar point while climbing, it needs to accelerate in order to compensate for the decrease in air density. Therefore, besides drag also this acceleration work needs to be subtracted before the remaining thrust can be used for climbing.
First let's clarify terms:

x$_g$, y$_g$, z$_g$ :  Earth-fixed coordinate system
x$_f$, y$_f$, z$_f$ :  Airplane-fixed coordinate system
x$_k$, y$_k$, z$_k$ :  Kinetic coordinate system where x is the direction of movement
L$\;\;$ : Lift
D$\;\;$ : Drag
T$\;\;$ : Thrust
m$\;\:$ : mass
$\alpha\;\;$ : Angle of attack (between the x-axes of the airplane-fixed and kinetic coordinate systems)
$\gamma\;\;$ : Flight path angle  (between the x-axes of the earth-fixed and kinetic coordinate systems)
$\sigma\;\:$ : Thrust angle relative to the airplane-fixed coordinate system
$v_{\infty}$ : Airspeed
The polar point should be the one for optimum climb speed. There is also one for optimum climb angle, but this simplification is justified. It also helps to make the math easier, since propeller aircraft climb best at the polar point where minimum power is required to maintain flight. This is at
$$c_L = \sqrt{3\cdot c_{D0}\cdot AR\cdot\pi\cdot\epsilon}$$
with
$c_L\;\;$: Lift coefficient
$c_{D0}$ : Zero-lift drag coefficient
$AR$ : Wing aspect ratio
$\epsilon\;\;$ : Wing efficiency factor
The zero-lift drag coefficient of propeller aircraft is around 0.025 to 0.04, with the high value for fixed-gear aircraft and the lower for those with retractable gear. It increases slightly with altitude due to the decrease of the Reynolds number from the drop in temperature. Here you need to pick a value which is appropriate for each specific aircraft.
Staying at the same polar point also means that weight will influence only the speed at which the aircraft climbs best, not the lift coefficient. The speed $v$ will change with the square root of the weight difference, because
$$v = \sqrt{\frac{m\cdot g}{\frac{\rho}{2}\cdot S_{ref}\cdot c_L}}$$
with $S_{ref}$ being the reference area of the aircraft and $\rho$ the air density.
Next to the correction term $C$ for acceleration. It depends on the local speed of sound, the gas constant for humid air $R_h$ and the temperature gradient (lapse rate $\Gamma$) of the atmosphere. This answer explains in detail how it is calculated and I repeat here only the result for standard atmospheric conditions:
$$C = 1 - 0.13335\cdot Ma^2 + \frac{(1+0.2\cdot Ma^2)^{3.5}-1}{(1+0.2\cdot Ma^2)^{2.5}}$$
with $Ma$ being the ratio between flight speed and local speed of sound.
Now your climb speed $v_z$ becomes $$v_z = \frac{v}{C}\cdot sin\gamma = \frac{v}{C}\cdot\frac{T\cdot cos(\sigma)-D}{m\cdot g} = \frac{P\cdot\eta_{prop}\cdot cos(\sigma) - D\cdot v}{C\cdot m\cdot g}$$
with $\eta_{Prop}$ the propeller efficiency and $P$ the engine brake power at the given altitude and throttle setting.
This leaves a bunch of unknown variables in order to correctly calculate the climb rate:

engine power
aircraft zero-lift drag coefficient
propeller efficiency

Therefore, it will be best to look up the possible climb speeds at several altitudes and power settings from each POH and to interpolate between those values. Or you settle for an approximation and use rule-of-thumb values for the unknown parameters.

for $\epsilon$ assume 0.8
for $\sigma$ assume zero
for $c_{D0}$ assume 0.026 at low and 0.03 at high altitude for retracted gear and 0.035 at low and 0.04 at high altitude for fixed gear.
for $D$ use $\left(c_{D0} + \frac{c_L^2}{AR\cdot\pi\cdot\epsilon} \right) \cdot\frac{\rho\cdot v^2\cdot S_{ref}}{2}$
for $\eta_{Prop}$ use 0.75 for a fixed-pitch and 0.8 for a constant speed prop.
for normally aspirated engines reduce power proportionally with density. For turbocharged engines assume constant power up to their critical height and reduce power in proportion to density above that. Let the users of your program set the throttle setting themselves.

Where you have performance charts available, compare your results with published figures and tweak the variables such that you get a good fit. For example, look at the published optimum climb speed and adjust $c_{D0}$ until your result, taken from the optimum lift coefficient, agrees. And so on. This should give you very useable results.


text:
Why doesn't the A320 pack flow indicate HI as it should?
When on ground with APU bleed on and both engines off I have noticed a number of times that the pack flow isn't at the HIGH setting why?
As per the FCOM it states that when APU bleed is on the PACK FLOW automatically goes to the HIGH position regardless of the PACK FLOW selector position. But a number of times I have noticed on the BLEED SD it doesn't indicate HI even though both PACKS are on why? Is there any reason for this or some system particularly I don't understand?

Related: How does Pack Flow work on the A320?

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text:
How do you program circular flight plans in GPS?
In a recent Buzzfeed article about aerial surveillance, I have seen a map showing perfectly circular flight patterns. Given how precise the patterns are, I highly doubt that the aircraft were being hand-flown.
According to the article, the planes used for this kind of survey work are GA (among others, Cessna and Pilatus PC-12 are mentioned in the article).
I was wondering how would you get to fly such a pattern using a GA-grade autopilot?
I did some research and so far the only way I could find was selecting a circular pattern in a G1000 equipped with the "Search and Rescue" additional SD card. However in this case it seems you can only have a circle where the centre of the circumference corresponds to a known waypoint (See third last page in this PDF manual), so probably that method doesn't offer enough flexibility for the purpose of aerial surveillance (e.g. what if there are no waypoints over the area you need to survey?).
Another way I imagine you could achieve something similar to a perfect circle could be by carefully setting aileron/rudder trim I guess, but I doubt you could hold a stable pattern over time just by using trim controls, due to wind, turbulence etc.
Does anyone have more insight on how you could achieve a perfectly circular flight pattern while being able to arbitrarily place the centre of the circle in any geographical location?

You can save waypoints based on coordinates.

@fooot I think your comment pretty much answers my question, if you post it as an answer I will accept it. Thank you!

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text:
What is the difference between an APU and an ATS?
Is there a big difference between what an Auxiliary Power Unit (APU) and an Air Turbine Starter (ATS) system actually does?
My understanding is that an APU provides power for the electrical systems of the aircraft and pneumatic pressure for air-conditioning and starting the main jet engines. An ATS provides starting power (compressed air) to a gas turbine engine.

Is the only difference that the APU also generates electricity for on-board electrical systems?
Would you ever have an APU and an ATS on the same aircraft? What are the use-cases for each product if they are mutually exclusive?

An APU can be also be found on many piston aircraft and can itself be a piston engine. Whether the power provided is electrical, mechanical, hydraulic, pnuematic or a combination has no impact on the fact that it is an APU. Neither does the end use of the power matter, as long as the power is supplemental or non-essential in normal operations, rather than the sole source.
An ATS is just an air powered starter motor used to spin up the turbines.

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text:
What dictates the A320's 'emergency ram air inlet' operation?
Why does the emergency ram air inlet flap open when delta p is greater than or equal to 1 psi on the A320?
Below is the extract I was reading from the FCOM. Why has the figure of 1 psi been set for opening or closing the flap?

The emergency ram air inlet opens
  ‐ If Δp ≥ 1 PSI: The outflow valve control remains normal. No emergency ram air flows in
  ‐ If Δp < 1 PSI: The outflow valve opens to about 50 % when under automatic control. It does not automatically open when it is under manual control. Emergency ram airflow is directly supplied to the mixer unit.

Please read carefully ...
Extract taken from my FCOM, Info accurate at January 2020:

An emergency ram air inlet ventilates the cockpit and cabin to remove smoke, or if both packs fail. The emergency ram air inlet valve is controlled by the RAM AIR pushbutton on the AIR COND panel. This pushbutton opens the ram air valve, provided that ditching is not selected.
When the RAM AIR pushbutton is ON : The outflow valve opens about 50%, provided that it is under automatic control and ΔP is less than 1 PSI. The outflow valve does not automatically open if it is under manual control, even if ΔP is less than 1 PSI. If ΔP is greater than 1 PSI, the check valve located downstream the ram air door will not open, even if the ram air door has been selected open. No airflow will then be supplied.

So based on that, the ‘door flap’ (ram air inlet), will open at any time, is the CHECK VALVE located downstream, the one that won’t open if the ditching pb or &P >1 psi...
The outflow will always be open (a little, in auto mode), that makes perfect sense, in order to &P becoming lower, and then that check valve (and the outflow), will open and the plane can be ventilated (smoke, fumes removal).

Greetings  thank you for further contributing to my question. Any and all doubts have been cleared with your answer and the answer given by @ymb1.


text:
On the new A320s when we do a brake check there is no need to call pressure 0 why?
Why do we have a give a pressure 0 call out when checking brakes while taxi on the old A320s but not in the newer A320s.?

I found an answer here: https://www.pprune.org/tech-log/456530-a320-brake-check.html
The complete fly by wire braking system apparently eliminates the check for residual pressure (check zero) of the older models, probably because the valve that determines which hydraulic pressure reaches the brakes is either no longer present or automatically tested anyway.
The new a320 also has a different PTU design which no longer barks...


text:
What do the different types of approach abbreviations used on the A320 MCDU exactly mean?
On the MCDU I have noticed after setting up the approach there are a number of different codes which appear next to the runway designator these are namely as below:
CI
CF
FI
CD
FD
Can someone kindly explain what these codes mean.

Hopes OP is setting up approaches in a flight sim, not the real thing...

CI = course to intercept
CF = course to fix
FI = fix to intercept
CD = course to DME
FD = fix to DME
These are AIRINC 424 leg types. You can find more information on them here

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text:
Why are the affected engine's bleed and pack switched off when there is an engine bleed under MEL?
My question mainly pertains to A320neo's equipped with PW engines. The MEL procedure states that the crew has to switch off the affected side's engine bleed, and its associated pack pushbutton to off.
One of the reasons given by my company is that with the engine operating at idle it may cause a reduction in the air supply and then lead to the automatic closure of the remaining bleed system due to a low pressure related failure.
However, this doesn't convince me, and I also tried raising it but I haven't gotten a response. The reason why it doesn't convince me is that one engine bleed can supply both packs, and the idle N1 automatically increases once the crossbleed is placed to open.


text:
I am 14 and want to be a pilot but don’t know how
Currently I am 14, turning 15 and live in Victoria. I have this aspiration to become a commercial pilot, but I don’t know how.
Should I start flying now? Should I get a private pilot license by 16? What should I study for VCE? Do I need to go into aviation for university, or is there a special flying university? How bad is the competition? What are all the stages of becoming a pilot starting from 15 years of age? Should i enrol in a flying school now?
I know it is a lot to answer, but I really am passionate. Thanks.
Erica

Is that Victoria, Australia? (If so: https://aviation.stackexchange.com/questions/8891/how-does-one-become-an-airline-pilot-in-australia?rq=1)

PPL is a very good choice to begin with your pilot career.
- You got quite a good knowledge which will be really usefull when you go for the CPL.
- You begin to collect flying hours (which is the most important thing to get a job).
- And you may realize if you are fit to fly (sometimes wishes don't match reality).

University is fine, but afaik nowadays airline companies don't ask for such degree when you apply for a job. However, it'd be a bonus.
Competition was hell years ago ('07-17), in particular for those with very low flying hours, never the less, currently companies are hiring a lot.
Sorry but I know nothing about VCE (I'm not aussie), but, if I can change your question to ' What should I begin to study to get ready for PPL/CPL?', then I'd say that you must get ready for the two subjects which trouble the most students. Principles of flight, and General Navigation.
I don't know if they are out of reach from your current knowledge, but, you may give it a try. I'd suggest you to use the Oxford books, or Jeppesen ones. Both are really good ones.
And about the stages, in my opinion:

PPL (fly as much you can)
CPL
Try to get a job (probably Flight Instructor (get FI license)
Apply for a company

Good luck

Your passion is great - if it doesn't go away you should have a successful career as a pilot.

Should I start flying now? Should I get a private pilot license by 16?

You certainly can, but there's no rush. It might be worthwhile focusing on your schooling first, because if you don't do well in that you won't become a pilot.

What should I study for VCE? Do I need to go into aviation for university, or is there a special flying university?

Maths and Physics are the big subjects and you'll need to study them through to year 12. English is also an important one. Other than that study subjects that interest you - you're more likely to score well on those. You do not need to go to university to be a pilot but it can be an advantage. Some universities offer a Bachelor of Aviation (usually management stream OR flying stream). But if they aren't an option for you any science degree will look good on your future CV. The flipside is that you'll be paying more than someone who just joins a private flying school, of which there are heaps in Melbourne, and you'll be a bit older when you start your career in earnest.

How bad is the competition?

You'll hear many people saying there's a pilot shortage, and others saying that is a myth. The truth is somewhere in the middle. There are lots of pilots who have recently come out of flight school who can't find their first flying job. That is undoubtedly the toughest step in a piloting career. But once you are more experienced and have specialized qualifications (for example, large seaplanes), you will be highly sought-after. Airlines will always have more applicants than jobs but in the last few years it has been really good for pilot hirings, especially compared with 5-10 years ago. What happens in the next few years though is anyones guess.

What are all the stages of becoming a pilot starting from 15 years of age?

The first step is to contact a flying school and ask for a trial flight. After that you decide if you want to continue, and one of the first things you should do is get a medical clearance. You then complete your recreational licence, your private licence (optional but recommended), then your commercial licence, with a whole bunch of theory exams throughout that. Following that you should get your instrument rating or instructor rating so you can get a decent job flying light aircraft. Do that for a few years and you'll have enough experience to apply for the airlines.
However there is a new route that is growing - airline cadetships.

Should i enrol in a flying school now?

This is a tough one to answer because there are pros and cons. My personal advice would be to wait. Qantas just announced that they are opening a large training organisation. Details are scarce but it will probably operate replace their airline cadetship scheme - meaning you train with them and get a job with them straight away, instead of flying light aircraft for a few years. If it's anything like their schemes in the past, they won't want people who have already begun flight training. You will need to have graduated high school or university before joining them, so I'd make that your first priority. If you miss out you can then enrol in another flight school or university, do an 18 month full time course and come out the other end as a pilot.


text:
How works the system of frequency for aircraft commercial Airline
Hello  I have to present a weather radar technology but i m block on  Air convention of communication.
I need to know how they exactly attribute licence to an aircraft and how all this aircraft can communicate without create collision between their communication .
Question one : Who attribute frequency for an Aicraft and how ?
- How are they attribute telecommunication frequency for commercial Aircraft .Each time they do a new fly someone give them a new frequency band ? They have a frequency band  for a specif numbers of fly ( E.g after 10 fly ) ?

Which authority give frequency band each countries ? but that mean if it's not a international authority you can use the frequency band only in this countries
Which authority decide into international zone what frequency band do you use ?

Question two : To much aircraft for number of channel
You have more than 20 000 aircraft use in the world however  I read you have 118–136.975 MHz Airband and only  potentially permitting 2,280 channels
so that mean a channel is use by more than one aircraft so what happen if two commercial aircraft have to use the same range of frequencies how their is not interference ?
My source :
 (https://en.wikipedia.org/wiki/Airband )
http://www.caa.co.uk/Commercial-industry/Airspace/Communication-navigation-and-surveillance/Radio-licensing/Radio-licence-categories/
Thanks you in advance for your supports.
Best regards,
CANAL Bastien

Frequencies for what purpose? You start off talking about weather radar, but you seem to be interested in communications frequencies. Are you interested in the frequencies used for air traffic control?

I think you have a misunderstanding on how individual radio frequencies are used.
Individual radio frequencies are not assigned to aircraft.  They are assigned to Air Traffic Control facilities like Control Towers or Area Control centers.
Each aircraft will have it's own "radio licence" but they can tune in any frequency that is needed for both transmitting and receiving. All aircraft in a specific area will use the same frequency as assigned by ATC. You may have 20 or 30 aircraft on the same frequency, but only one aircraft should be transmitting at any time.
There is a lot of congestion on the radios in a busy sector and "CPDLC" (Controller–pilot data link communications) is gradually being introduced in many areas. This allows ATC and the pilot to communicate directly via data-link text messages.
In some areas where there is no ATC control, aircraft can monitor or communicate on a common "air to air" frequency.  123.45 is used in some areas.


text:
Why is FL398 the REC MAX altitude on the A320?
On the A320 PROG page and in our limitations the REC MAX/ MAX FL is listed as FL398. What is the reason behind this ?

Related: What is the difference between Cruise and Service ceilings?

I just came across the answer in the AFM it states
"THIS IS THE MAXIMUM ALTITUDE AT WHICH IT IS POSSIBLE TO MAINTAIN CABIN PRESSURE ALTITUDE BELOW 8000 FT"

Green Dot Speed (GD) is the aircrafts best lift to drag ratio speed.
As altitude increases, the maximum thrust available decreases.
Looking at the graph beneath, if we increase our altitude and get closer to REC MAX then points 3 and GD move closer together because of the smaller thrust margin of the aircraft.
Having these points closer together means we could easily slip into a quick deceleration if speed is reduced. The REC MAX is calculated based on the service ceiling, aerodynamic ceiling and max certified ceiling and is considered as the safe upper limit.
Here is a nice article which covers this information in more detail:
https://www.airbus.com/content/dam/corporate-topics/publications/safety-first/Airbus_Safety_first_magazine_21.pdf

I've never heard of the phrase Green Dot.  I guess it's an Airbus thing?  In RJ land we just referred to it as Min Drag.

Yes it's a specific term used for the airbus. As the name would suggest it's just a simple green dot which appears on the PFD.

Is Single Engine Driftdown Speed on the AB based on GD or GD+ some margin?

If an engine fails on the airbus then the GD speed is recalculated as the drift down speed. It's handy how airbus simplify these things.


text:
Why does the flight controls check come before arming the autobrake on the A320?
As per SOP on the A320 we first perform the flight controls check and then arm the autobrake to max. What is the reason behind this?


text:
Why would smoke enter the cabin if the batteries are switched off before the APU flap closes?
In the A320 FCOM SOPs securing if the APU flap doesn't fully close smoke may occur in the cabin in the next flight
In the NORMAL PROCEDURES SECURING THE AIRCRAFT. It states that before switching off the batteries we have to wait for the APU flap to fully close if we don't and we switch offf the batteries before the flap fully closes it states that smoke may occur in the cabin during the next flight. Could someone please explain as to how smoke will occur.?


text:
What will happen to the IDG disconnection mechanism if we press and hold it for more than 3 secs?
I read in the Elec systems chapter that if we press and hold the IDG pushbutton for more than 3 secs it’ll damage the disconnection mechanism. What exactly happens? Also it says that not to disconnect it if the engine is not running as if we do and then start the engine it’ll damage the IDG. How does this happen?


text:
How does switching off pumps and putting on MAN switch resolve low pressure?

FUEL
  If the center tank is less than 200 kg (440 lb) for the flight: Apply the following procedure, if your airline is affected by FUEL CTR TK PUMPS LO PR cautions on ground or in flight when the center tank is less than 200 kg (440 lb):
FUEL MODE SEL pb sw ....... MAN
CTR TK PUMP 1 pb-sw and CTR TK PUMP 2 pb-.....OFF

I came across this while reading Normal Procedures. Could someone kindly explain as to how the centre tanks pump low pressure gets resolved by following the above mentioned procedure?


text:
Why is deploying speed brakes not recommended with the flaps extended?
I read this in the normal procedures section of the A320 FCOM. Why is it so?

When the speed brakes are deployed, extending the flaps beyond FLAPS 1 may induce a slight roll movement, and in calm conditions a small lateral control asymmetry may remain until disturbed by a control input or by an atmospheric disturbance.

@ymb1 could you explain this phenomena?

@ymb1 it appears specific to the A320. At least in the B777 FCOM, I have: "There is no limitation for extension of speedbrakes in a landing configuration".


text:
Could someone please explain what is thermal oxidation of the carbon brakes?
In my company SOP after landing we don’t switch on the brake fans immediately after the HOT annunciation comes on on the BRAKE FANS push button. Instead we are told to wait for a period of 5 mins after landing to allow for thermal equalisation of the brakes and to prevent oxidation of brake surface hotspots.
What exactly does this mean?

Carbon does always react with oxygen. At room temperature, the rate of that reaction is low, but measurable. If the temperature goes up, the reaction rate goes up too... Big coal piles, for example, use to get warm by slow oxidation, and if not doused with water, may spontaneously catch fire...

"Furthermore,  after  heavy braking,  use  of  the  brake  fans  could increase  oxidation  of  the  brake  surface  hot  spots,  if  the  brakes are not thermally-equalized." (§4.2.3 of How to properly operate the carbon brakes?). So wait for highest temperatures to decrease before adding oxygen because oxidation is accelerated by temperature. Also (probably) prevent other oxidants and FOD to enter the brakes

Did my answer help at all?

Catalytic oxidation of carbon occurs when a catalyst, such as an
  alkali metal(s), is present. When a catalyst is present, the
  temperature at which thermal oxidation occurs is lowered. Airplanes
  equipped with carbon brakes are susceptible to catalytic oxidation
  caused by exposure to alkali metal runway deicers. - Boeing Aero
  Magazine

Brake manufacturers produce Oxidation resistant brakes. The effects of can be obtained by using carbon brakes, or using a coating on the brake rotor and friction surfaces.
Best practices for carbon brake application according to Airbus.

@fooot I fixed that. Thanks for the comment.


text:
What will happen if we start the A320 engines but we don't wait for the amber crosses on the E/WD to disappear?
My logic is that we should wait for the sensors to register the present indications so we have a proper idea of what state the engine is in particularly the EGT if we have to consider a manual start.


text:
Why can't we use APU bleed air for wing anti ice on the A320?
The question says it all. While reading I came across this that we can under no circumstances use APU bleed air for supplying wing anti ice? Any reason?


text:
Why can the A320 VAPP be decreased down to VLS?
I read in the Airbus A320 FCTM (p349), normal procedures descent section:

The flight crew can insert a lower VAPP in the MCDU PERF APPR, down to
  VLS, if landing is performed without A/THR, without wind and no ice
  accretion.

You have no margin against a stall condition. Why is that possible to decrease VAPP till VLS?

I want to start with a counter question? What does the regulations say about your landing speed? Does it say, it is Vls (lowest selectable speed) or Vapp (approach speed). You will find neither of these speeds. As a matter of fact, Vls is strictly an Airbus term. You would not find a Vls speed in any other type of aircraft or in the regulations.
The landing speed for a CS-25 aircraft (large aeroplanes), which is the category of Airbus A320 is Vref (Reference landing speed). Not Vls or Vapp.
According to FAA, Vref is defined as:

Reference landing speed means the speed of the airplane, in a
specified landing configuration, at the point where it descends
through the 50 foot height in the determination of the landing
distance.
A stabilized approach, with a calibrated airspeed of not less than
Vref, must be maintained down to the 50-foot height.
(i) In non-icing conditions, Vref may not be less than:
(A) 1.23 Vsr0 (stall reference speed in landing configuration);
(B) VMCL

Vls as I have said before is an Airbus specific speed and in landing configuration, Vls is 1.23 Vsr0. If we look at the Vref definition above, we can see that when coming in for landing in any Airbus aircraft Vls = Vref. So, is there a problem in reducing the speed to Vls on final approach? The answer is simply no. If you look at the landing speed table in the A320 QRH (image below), you will see that Airbus has clearly mentioned Vls is Vref when landing.

The next part to clarify is that Vls is not the stall speed. It has a good amount of margin from it. Usually in the range of 1.23 to 1.28 times the stall speed, depending on the aircraft configuration and phase of flight. To give you a real life example, a few days back, we took off in a heavy A321 and in a turn as we retracted the flaps, the speed momentarily went below Vls. The aircraft did not stall and we made it just fine. It was a non event.
Now, let us look at the Vapp (approach speed). This speed is derived from the Vref. The Vapp is basically the speed that we get when we add some corrections to the Vref. Why do we add corrections? To compensate for things like gust and ice, so that we do not lose aircraft energy when for instance there is a sudden reduction in the headwind in a particularly gusty day. In A320, we also add about 5 knots to Vref, if the landing is done with autothrust on because sometimes the autothrust lags in reacting to changes in conditions which can deplete the air speed. We call these corrections approach corrections (Appr Cor). This gives us:
Vapp = Vref + Appr Cor
Here is how you determine the approach correction for A320 to get Vapp.

There are some circumstances where you are required to reduce speed to Vls during the approach. And one of them is when you have to do an overweight landing. The checklist for the procedure (attached below) asks you to reduce speed from Vapp to Vls when coming over the runway threshold. If you are an A320 pilot I am sure you would have done overweight landings in the simulator and in the final part of the landing, you would have asked (I hope) the Pilot monitoring (PM) to select speed and set Vls. This reduces the impact forces on landing as it reduces the kinetic energy of the aircraft.


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On the A320, why is it not recommended to use the HP ground unit when the APU Bleed is on?
Can someone explain what the HP ground unit is used for? And what damage happens to the bleed system if it is used?

Sure I'll do it here on out


text:
How does a higher temperature when programmed in the FMGC affect REC MAX FL?
While I was reading the FCTM I came across this line mentioned below.

An increase in the Outside Air Temperature (OAT), that results in a decrease of the REC MAX FL.

I wanted to know if we enter a higher than normal temperature for a particular FL or we even forget to put the minus sign in front of the temperature value (our older A320s with Honeywell FMS accepts the temperature without the minus sign) how does this cause the FMGC to compute a lower REC MAX FL?

Without having access to the documentation right now, I believe entering a higher temperature would cause the FMS to calculate the density altitude to be higher for each geometric altitude (it assumes a standard ISA temperature lapse). As the FMS thus assumes „the day to be hotter“, essentially, it would reduce its assumptions regarding aircraft performance capability and would therefore reduce its altitude predictions and recommendations. Just my speculation, hence not added as an answer.

@CptReynolds you are correct the FMGC assumes an ISA model until we modify the temperatures and tropopause level.  I think you might be right as it may be linked is there any way to confirm your answer if right or wrong?

FMS calculates REC MAX in cruise by calculating temperature from actual OAT and TROPO inserted in INIT A page. It assumes standard -2C/1000ft until inserted tropopause altitude which after it uses constant temperature.
During climb it calculates temperature profile from inserted tropo/temp. If your REC MAX seems to be off during climb check the inserted values. Also, when A/C reaches CRZ ALT entered to PROG page it starts to use measured OAT at once, so REC MAX can change suddenly if it was off in INIT A page.
Note that REC MAX is only function of A/C weight, TROPO and OAT. Cost Index does not affect REC MAX.

Could you please expand some of those acronyms? I feel just as lost as when my son in the Army starts rattling stuff off...

Yes it is the consequence of the predictive calculated air density, but once in flight the actual temperature is updated and the recommended max FL too

are you confirming CptReynolds answer?

Yes, but more precisely bus driver answer


text:
On the A320 why do we follow this particular sequence of taking flaps and gear?
First we take flaps 1 then 2 after that we lower the gear followed by flaps 3 and full. My thinking is that this will avoid any GPWS warning is that it or there is something else also to it.?

The procedure is somewhat similar in small GA aircraft with retractable gear. I was always taught that the sequence was "flaps-flaps-gear-flaps" and then another gear check on short final.

There is not a technical reason. The procedure gives the best and the most optimum deceleration rate on the approach. Think of this. With flaps 1 already set, your S speed (minimum maneuvering speed with flaps 1) will be at like 185 knots (aircraft weight at about 63 tonnes), which is pretty close to 200 knots. If you put the gear down after flaps 1, a lot of unnecessary thrust has to be added to maintain this minimum safe speed. But if you put in flaps 2 before the gear, the aircraft can be safely decelerated to about 145 knots. To maintain this low speed, a lot less thrust will be required. Hence, if you put the gear down after flaps 2, a large thrust bump would not be needed, making the ride comfortable and more efficient.
The other reason is that in all transport category aircraft I have flown, the landing flaps come the last in configuring sequence. In A320, both flaps 3 and flaps FULL are approved landing settings. So, putting the gear down before the final setting makes more sense. The reason why the final flaps come last is to prepare the aircraft for a go around. So, it is always a good practice to put down the final stage of flaps only when you are fully committed to the landing. Flaps are quite detrimental to go around performance. That is why in Airbus, when you initiate a go around, the pilot flying calls out: GO AROUND, FLAPS (i.e command pilot monitoring to take flap up by one stage). When I flew Dash 8s the call out was: GO AROUND, MAX POWER, FLAPS 15 (if the landing is performed at flap 35). As you can see, the flaps up command always comes before the landing gear.
The real question here is, can you modify the sequence? The answer is yes, you can as long as you maintain a safe operation. I have had to lower the landing gear without any flaps twice in my time in A320. One time, we were high and fast (about 15 miles to the runway) and we realised, that if we do not act up soon, we will end up in an unstabilised approach. So, we put the gear down, and extended the speed brakes. The gear generates a lot of drag and together with the speed brakes, the speed bleeds off quite fast. As the speed came to flaps 1 speed we put down flaps 1 and configured flaps to FULL in sequence. The next time it happened, there was a notorious tail wind pushing us on the approach which made the deceleration difficult. Again, selecting the gear down first helped us to ensure a stabilised approach and to avoid an unnecessary go around. Thus, within a safety margin, you can always change up the configuring sequence if it is ever required. The best is to always follow the SOPs, but as a pilot you should always know what to do if something happens outside of the book. That is the mark of a good pilot.

You would want to start with flaps/slats. The landing gear slows the aircraft down like an airbrake, and you'll need a higher lift coefficient to retain enough lift. Slats are a safety feature that allow for a higher angle of attack for the main wing, flaps provide a higher $C_L$ by themselves. So you start with a higher $C_L$ and the safety of the slats, then deploy the gear which slows you down, then delay more flap/slat at the lower velocity.
Deploying full flap/slat first and then deploying gear is also not a good idea: speed will be slow already at max flaps, gear deployment brings a significant further deceleration which may have an impact on safety, definitely on continuity throughout the landing process. You are in a queue with lots of others at a busy airport, and want to keep the array of craft flowing without sudden decelerations.

I know each aircraft will have Vmax limits for each config. Is the flaps/slats limit usually higher than the gear limit? And is the gear limit usually higher than flaps full?

I reckon the procedure is just for Best Practise. It could probably be done in a different order without breaking the aircraft, but the procedure of the OP makes the most sense.

Found an A320 manual online. VLE/VLO are 280/250kt and VFE is 230kt for the 1st position (slats only). So you're correct, it's not due to design limits

this is speculation, but if you ask why we lower gear between F2 and F3, I think Koyovis is getting quite close to the potential answer:
Each configuration has a reference speed: Green Dot,  S speed, F speed. The biggest difference is between S and F ( ie after deploying flaps 2) , that is: this is where aicraft will decelerate the most from around the 180+ kts S-speed to the ~140 something F-speed.
This can take quite a while to decelerate, so it might be a good ideea to use this time to lower the gear (since hydraulics are now free) and even use that extra drag from gear to decelerate.
Mind you, you can still lower the gear at the same time as lowering the flaps, it's just extra strain on the hydraulics so most people will try to avoid making that habit.
Also, remember it is not prohibited to lower the gear much earlier ( eg. if you require extra drag on the approach), even in clean config.There used to be a limitation of FL250 for deploying gear, but that has recently been removed.
You could also delay gear down until after flaps full if there is an operational necesity. The only real limitations is to be below Vloe (250kts/M0.60) and you should try to get gear down preferably before GPWS kicks in (750ft)

There used to be a limitation of FL250 for deploying gear Are you talking about a regulatory limit? In the US?

@TomMcW , no it was an Airbus 320  limitation in FCOM


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Why is it not recommended to hold the nose up on the A320 after touchdown?
I was recently told by a trainer in my airline that on the A320 if we hold the nose up after main gear touchdown then the flight control laws logic will memorise that pitch attitude after 5 seconds and will hold it there. Can anyone provide clarity on this? I have read the FCTM and know this is not a recommended procedure.

I do not think what your instructor said is true. The flare mode activates at 50 ft radio altimeter height, where auto trim is cancelled and the pitch attitude  memorized by the Elevator Aileron computers (ELAC). At 30 ft, the memorized attitude is used as a reference to push the nose down by 2 degrees over a period of 8 seconds. The flare law is necessary to give the pilots a conventional flare experience. Because Airbus aircraft are pitch stable, if there is not a flare law, every time you pitch up to flare, that pitch attitude will be maintained and there would not be the normal sink rate (visual aid to commence the flare) you see when you try to land a non fly by wire aircraft. The flare mode changes over to ground mode, when the aircraft pitch attitude is less than 2.5 degrees and the aircraft is sensed on the ground for more than 5 seconds.
A prolonged nose up attitude would not make the computers memorize any pitch attitude. The flare mode is done with memorizing attitude at 50 ft and there is not a nose down pitch applied by the computers either, as it is done with it from the point aircraft passes 30 ft and the 8 second count down is over. The only thing that will happen is that the aircraft will not enter the ground mode, but will remain in flare mode and the trimmable horizontal stabilizer (THS) would not reset to zero. As flare mode is a direct stick to elevator relationship, the elevator moves with the corresponding stick demand. So, if you pull back on the stick, the elevator will move up and the pitch attitude will increase depending on the aircraft energy level.
The aircraft FCTM recommends the pilots to smoothly fly the nose wheel onto the runway. It says fly, not drop. After the main wheels touch the ground, you should try to hold the nose wheel and slowly make it touch the runway. I have seen the nose tilted up for more than 5 seconds and have done it myself as well, because if you let go off the nose too quickly, it tends to smack the ground quite firm. In these situations, the aircraft always behaved normally as you expect it to. But yes, it important not to over do it, as it can lead to a tail strike. That is the only danger associated with it. So, you should properly modulate your pitch up inputs to hold the nose off after landing.
A320 FCTM

@ymb1 In my airline's A320 manual which is provided by Airbus states: Flare mode is essentially a direct stick-to-elevator relationship
(with some damping provided by the load factor and the pitch rate feedbacks).

Even in a conventional aircraft, with a direct stick to control surface relationship, you are essentially commanding a pitch attitude in the longitudinal axis. So, what was written in the safety first article is not incorrect. It is just worded differently. Safety first articles states: 'A pitch sidestick deflection corresponds to a
commanded pitch attitude.'

Why would it slam down. I have been flying the A320 for quite some time now. I have kept the nose up after landing for more than 5 seconds and I have never noticed a change in aircraft behavior. How do you think normal airplanes land then? Their THS does not automatically reset. Does it lead to a tail strike? The pilot has to hold off the nose to prevent it from slamming. The flare in Airbus aircraft is very very conventional.

The other thing to keep in mind is as we flare, the thrust is pulled to idle and the speed reduces. The aircraft nose naturally tries to come down and you hold it. Even if the 5 seconds pass and if the nose is greater than 2.5 degrees the flare law would not activate as it did as at 50 ft. And how are the computers going to pull up the nose of an aircraft that has no energy (thrust at idle).

What do you need for flare law to activate? 50 ft radio altimeter height. At 50 ft it memorizes pitch and at 30 ft it gives a small pitch down. Even if the aircraft does not go into ground mode, the flare law would not reactivate as it did at 50 ft.


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Why would the outer tanks fuel on the A320 be colder than the inner tanks?
I have noticed in a number of instances during long flights typically over 5 hours the fuel in the outer tanks on the A320 are colder than the fuel in the inner tanks. This goes against the system logic as warm fuel gets first recirculated to the outer tanks then the inner tanks.
However in the FCOM it's mentioned in a note if the outer tanks are full, fuel spills over into the inner tank, does this mean that the warm fuel is now going directly into the inner tanks? Also can any other variables play a factor like fuel temperature on ground?


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Why is EGT decreasing on a jet engine when the generators cut in (take over)?
Is the EGT decrease related to the generators cutting in or is it related to the fact that the fan is now providing enough ventilation air for the engine?
When I say cut in I mean that the engine driven generator has taken over in supplying the electrical load from the APU driven generator.

Which jet engine?

Well, the simple answer "no", since it's the rise in N2 (and therefore more air through the core) which causes the EGT to  fall.  Put it this way, if you remove the generators, the engine will start in exactly the same way.

@koyovis its the IAE V2527-A5

@ymb1 yes when I say cut in I mean that the engine driven generator has taken over in supplying the electrical load from the APU driven generator.

EGT on some engines is proportional to the engine developed power, cutting the generators reduces the needed power, thus reduces the EGT


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How does a 10 second delay after switching on the APU BLEED prevent an engine stall while carrying out a one engine taxi on departure in the A320?
My question mainly pertains to the delay of 10 seconds. As per the A320 FCOM when performing a one engine taxi at departure before starting engine 2 a 10 second delay has to be catered for after switching on the APU BLEED. The reason mentioned in the FCOM is as follows:
"Wait 10 s before the ENG 2 start, in order to ensure that the BLEED system valves are no longer in transit. This time delay will prevent ENG 1 stall"
How does the time delay prevent eng 1 stall is what I can't understand. Attached is a picture of the official FCOM excerpt.

I'm not A320 qualified – but bleed air valves are often electrically driven but pneumatically operated. Depending on available bleed air the valves need some time to close or open. As you just configured the bleed air system to use APU bleed air to start the engine, the eng #1 bleed valve might not have closed yet. An engine start has a high air demand and therefore might extract too much bleed air from eng #1 with might lead to engine stall. The 10s wait time makes sure that the eng #1 bleed air valve has closed and you don't run into trouble there. As said – I'm not A320 rated, it is a guess

As stated in the quoted material it’s not the time delay that prevents stall- it’s the bleed valves being in transit that could lead to stall. Your real question is therefore “How would attempting a #2 start with the bleed valves in transit lead to a #1 engine stall?”

@Jim why dont you Formulare an answer on this insight


text:
What is the average number hours flown annually by a commercial cargo aircraft?
I'm hoping someone has already performed some initial research that might support some preliminary economic models for an aircraft design project.


text:
How do airplanes maintain separation over large bodies of water?
I have read that the oceans are big enough that ground radar stations only reach so far out. I assume that means after a certain distance from the coast they leave ATC services. Do airplanes employ any techniques to avoid traffic separation outside of ATC services aside from following their flight plan and the rules of the airway they are flying, and for an emergency backup the TCAS system?

I wonder if there has EVER been two aircraft that plain collided when in open transit far from airports?  It seems hard to believe it has ever happened.

@Fattie Great question.  The answer is: YES, in 1956 over the Grand Canyon and as the article notes: it changed aviation forever because it resulted in the creation and empowerment of the FAA and the NTSB: https://time.com/5885096/airplane-collision-history/.  The Wikipedia article has more on how it happened: https://en.wikipedia.org/wiki/1956_Grand_Canyon_mid-air_collision

@Fattie Gol 1907 as well, over the Amazon in 2006: https://en.wikipedia.org/wiki/Gol_Transportes_A%C3%A9reos_Flight_1907

And another one: https://en.wikipedia.org/wiki/1997_Namibia_mid-air_collision

I wonder how gps and transponders have affected the protocols.

Also see Wikipedia for a (non-exhaustive) listing of mid-air collisions: https://en.wikipedia.org/wiki/Category:Airliner_accidents_and_incidents_involving_mid-air_collisions.

Also keep in mind that most transcontinental aircraft have their own radar. It's intended/used primarily for weather, but another aircraft at close range will show up quite clearly as well.

They don't leave ATC services when they enter oceanic airspace, but the service provided is no longer based on radar. Instead separation is maintained by following procedures. For example, that means that only certain routes (tracks) are flown, with 15 (or 10) minutes separation between aircraft on those tracks.   The aircraft strictly adhere to speed instructions and report to ATC at specific points.
Another form of separation is vertically,  just like in a radar environment,  by assigning different altitudes (flight levels) to aircraft.
The voice communication is over HF and is supplemented by data link over CPDLC / ADS-C via satellite link.

What about Flight Level seperation?

@MikeBrockington same. GPS is so ingrained in flying nowadays that they can keep the height to a few meters (+/- turbulences etc of course). But even without GPS you could be able to keep your flight level to enough precision

@Hobbamok I think that flight levels are determined by barometric pressure.

@MikeBrockington sure, Flight Levels are used just like in a radar environment.

@Hobbamok GPS is not used for vertical navigation in the en-route phase. Only pressure altimetry is used (Flight Levels).

To expand on DeltaLima's answer:
They use routes called the NATs (North Atlantic Tracks), which can differ each day depending on weather and wind speeds. Each track is a set of coordinates. A pilot will do a position report at each coordinate or every 10 degrees of longitude. The aircraft has to get special clearance to fly oceanic about 30 minutes before crossing the entry waypoint for the NAT. Each NAT is 60 NM apart.
To clarify a bit more, HF radio is used to communicate, since it has a longer range than VHF, but is much noisier. This is where systems like SELCAL come in. SELCAL stands for SELective CALling, which allows the pilots to lower their radio volumes. Each aircraft has a unique SELCAL code which consists of four characters that can be made up of A, B, C, D, E, F, G, H, J, K, L, M, P, Q, R, and S. When a controller wants to talk to a pilot, they send a "ping" to the aircraft, which plays a sound in the cockpit to tell the pilots to get on the radio. Position reports can be done via HF radio, or increasingly via text (CPDLC/ACARS), taking advantage of ADS-B/C. These communication systems are pretty complicated, so I recommend you search for them on the web or look at the sites I linked below.
Aircraft are required to be 1,000 feet apart vertically. Eastward flying aircraft have odd altitudes such as 37,000, 39,000, 41,000, etc, while westerly flights will be the opposite. They are also required to be about 10 minutes apart from each other.
Gander Radio (notice not "Radar"!) controls much of the North Atlantic airspace from Gander, Newfoundland, Canada. Shanwick is another major Radio station. New York controls further south, along with Santa Maria controlling relatively small airspace.
There is a similar system over the Pacific ocean, with stations in Anchorage, Alaska, and Oakland.
Links:
I highly recommend you read this article about North Atlantic Tracks, and this one too.
You should at least watch this video, it's only 3 minutes, and it's summarized well:

More about ADS-B
More about SELCAL
More about position reports
More about ACARS:

Hello tizmataz77, welcome to aviation.stackexchange.com! Nice first post, I hope you make more of those.

@DeltaLima Thanks!


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Why do airplanes bank sharply to the right after air-to-air refueling?
Whenever I see videos on YouTube they bank really sharply to the right after disconnecting from the tanker. Why wouldn't they do a more shallow 30-degree bank?
See this video for reference:

Rule Of Cool.  Normally they do a barrel roll.

I don't see "sharply" TBH

@mayou36 it is subjective. What is 'sharply' for a landlubber layman might be a soft bank for an airborn flyer. Who knows? I don't. Unless math gets involved and we define the 'sharply' threshold, it is fine to use these terms IMHO

The point is, there's nothing abnormal about what's happening here, which is what OP is suggesting.

@Mindwin For an F-18, that's about as careful and gentle as it gets.  I doubt the manoeuvre made the g-meter move at all.

The premise of the question is wrong. That's not a "really sharp" bank. It's both shallow and slow; especially if you think in terms of a fighter jet. I would argue that the bank is not "sharp" even for a recreational aircraft.

oh my goodness, can we get rid of these horrid overlays that prevent me from seeing a big chunk of the video?  what was someone thinking???

"...to the right". Seen from where?

Because fighter pilots tend to be conservative.

Fighter jets are very maneuverable, so they may make anything from a shallow bank to a breakaway maneuver. The breakaway is a standard way for fighter jets to exit a formation. It provides a way to safely and quickly gain separation from the other aircraft.
In this case the bank is fairly shallow, but when the aircraft disconnects they are already in a shallow right turn, so the total bank angle is a bit larger.

That was not a breakaway maneuver, that was just moving to the outside of the formation.

The video absolutely does not show a breakaway manoeuvre.  This is incorrect.

@ymb1 Also, see the second fj in formation, he does a much sharper turn away.

Doesn't really look all that aggressive to me, either way the fighter and the tanker are very vulnerable while refueling. Usually there is more than one aircraft waiting to refuel, so the goal of this game is to run as many of the aircraft in formation through refueling as quickly as possible.
In order to do that, you need to get your wake out of the way for the next guy to get a smooth approach to the basket. As Fooot says in his answer, the pilot is using a standard "breakaway" maneuver to get out of the formation and wait for the other pilots in the flight to get the fuel and continue with the mission.
Plus you just got a full tank of fuel in the world's funnest military equipment...

I agree it doesn't look very aggressive, and therefore wouldn't call it a "breakaway".  In fact this pilot was not even leaving the formation, he simply moved to the right side and stopped there.  Perhaps waiting on a wingman to top off...

A breakaway is for... breaking away... quickly.  The plane did not leave the formation.  It did not move to the side quickly either.  It just casually repositioned itself in the formation.

Different air forces may operate with different conventions, but right from basic flight training the RAF classifies banked turns of 20 degrees as "gentle," 40 as "medium" and 60 as "steep," and the most commonly used are "medium".
Ref: The RAF Basic Flying Manual (1952 edition) - https://www.t6harvard.com/wp-content/uploads/2017/11/Chapter-3.pdf page 26-27.
The video is just a 40 degree banked turn.
The aircraft have no problem handling the G loads in 60 degree banked turns, and there are not going to be any complaints from passengers in Business Class that the flight crew spilled their gin and tonic!

Even most light piston aircraft have no problem with 60 degree banked turns. It's just 2 Gs if you hold altitude. That's nothing for a fighter.

They do this because there are 3 main parts to an air to air refuel:

port observation where they wait to be refueled in a line.
refuel area where they actually get refueled.
reform area where they wait for the rest of the squadron.

After the refuel, they will bank the right to go to the reform area and will wait for the rest of there squadron. Once everyone is refueled then they break from the tanker.

A jet joins on one side of the tanker then when its turn comes moves behind to tank then when finished, clears off to the other side.  Bear in mind a whole formation may be tanking and need to flow through the same process.  The turn after tanking is not a hard turn in fast jet terms.

many people have already explained

Others seem to have answered the why such a sharp maneuver part of the question, so I will answer the why to the right part. Collision avoidance in aircraft is always by turning to the right when possible. Keeping the formation in such a way that the pilot can always escape to the right is probably done to ensure safety, as it lines up with the engrained training.

If two (and only two) planes are re-fuelling simultaneously, then the left-hand aircraft will  likely break to the left initially.

Two aircraft must either be flying in formation, or be far apart, to be safe. While the fighter is in the process of leaving the tanker, it is neither. It therefore moves away quickly using the standard breakaway manoeuvre. Bank really sharply? The video showed a positively leisurely turn in the circumstances.
Why to the right? It's standard to approach on the left side of the tanker. That's where other fighters waiting and approaching to refuel will be, so the left is a good side to avoid.

I agree it was leisurely, but "leisurely" and "breakaway" don't go together...

To gain as much seperation as quickly as possible.


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How common and dangerous are fume events?
I’ve been hearing about fume events where engine oil containing tricresyl phosphate as an additive can leak onto the HVAC packs and enter cabin air. These organophosphate are incredibly toxic and are used in nerve gases. There are even cases where pilots have died such as here (AVHerald) and here (BBC).

Thank you for bringing this issue up, however, please consider to ask not for an opinion but for hard facts. Then this question will fit better with the preferred way of asking questions here.

Wow. Is a situation with the pilots flying the next few days common or recklessness on the airlines' part ? Noone could guess they might still have medical issues ? (like internal bleeding as it turned out)

You may ask only one more specific  question: hoxw common are those event? what kind fume event exists? what are the risks associated?...

The AVHerald article you linked to pretty much as the answer to your question:

How common are they?Nearly 2,000 events a year in the US alone.

[According] to the Kansas State University Research there have been 5.3 fume events per 24,000 daily flights in the USA or 1955 fume events a year. However, only 6 fume events per year get reported to the FAA.

How dangerous are they?In extreme cases, they can lead to death, but even mild cases diminish flight crew capabilities.

I’d say I agree with this but I’ll wait for a few other answers to mark one. Mainly wanted to post to see what other people think but as you said that’s not appropriate.

In the comments several people report smelling fumes after a compressor wash. So there seem to be two sources for "dirty socks" smell: Oil heated above 700°F and solvents remaining after a compressor wash.

On AV Herald, there is almost a fume event every day, and indications are many don't get reported. Some aircraft seem more susceptible to fume events, e.g the BAe146. See https://www.theguardian.com/science/2017/aug/19/sick-crew-toxic-air-planes-frequent-flyers-ill. The article also mentions the Aerotoxic Association: http://www.aerotoxic.org. Maybe a good reason to fly on the 787, which is the only aircraft not to use engine bleed for the cabin. https://www.telegraph.co.uk/travel/travelnews/6839234/Boeing-787-Dreamliner-is-a-breath-of-fresh-cabin-air.html

Wow, every day, that’s quite often. I have heard that about the bae146. Now if only I could get Jet Blue to fly the Dreamliner from Boston to Sourh Florida.

On AvHerald I'm sure fume events are the most common thing reported. A quick search for "fume" returned 14 so far this year. Nine of them are categorized as accidents, meaning someone, passenger or crew, was hospitalized. It's a big problem and it really doesn't get enough attention imho.


text:
Can anyone suggest a good book on aircraft performance?
Im trying to find a good book pertaining to aircraft performance and I have come across a book by PJ Swatton quite a number of times while searched on the internet.
Is this a good book or are there any better books?

In addition, it's way too broad. What kind of "performance?" Powerplant, aerodynamics, stability and control, etc.? Of a particular aircraft or class of aircraft? Without narrowing it down, your question literally asks about the entire body of aviation knowledge developed over the last >100 years.

"Aerodynamics for Naval Aviators" (free PDF or Amazon) is a great introduction, and from there you can dive into more engineering theory books.

While the question isn't a great fit for Av.SE, this answer is absolutely spot-on. For those looking for more depth than a basic PPL groundschool, this book is pretty much the canonical standard.


text:
List of Non Tower Airport - World?
May I know the Non-Tower Airports throughout the World - List. Please ?

I seriously doubt such a thing even exists.

There are literally thousands of them.

If you need a list of all non-towered airports in the world, do following:

Visit the data section of ourairports.com
Download the files airports.csv and airport-frequencies.cvs
Read through every airport in the first file and search for the respective frequencies in the second file
If there is no tower frequency for the airport you are iterating through, write the ICAO-Code into another file
When finished, you have a list of all non-towered airports

If you have programming experience you should be able to do this.

This is a good piece of teaching somebody to fish.


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How are foreign militaries regulated in the USA?
I believe the US military is not officially subject to the FARs, but what about foreign military aviation?  What about aviation activities of the various National Guard outfits?
Example...the Belgium air force operating a squadron of C-130's during a training exercise held in the USA.

Yes, foreign military operating in US airspace and utilizing US civilian airfields.

Example...the Belgium air force operating a squadron of C-130's during a training exercise held in the USA.  My first time, apologies for the missteps.

I belive all aircraft operating in civilian airspace (military included) must at least have proper equipment aboard and follow civilian regulations on airspace etc. Even US military planes cary civilian transponders and radios for this reason. They can however operate without those things with prior approval.

The overall issue we are faced with is whether or not foreign military aviation activity in the USA is considered "General Aviation" or "Military" by the FAA.  Figured stipulations on whether or not they must comply with the FARs would be definitive.  Same issue with Air National Guard aviation activity.

As to flight rules(different than aircraft and pilot certifications) US military aircraft are very much subject to all the same rules as civilian aircraft. They just bother with the paperwork to get special permissions for stuff like block altitudes for convoy flights. For fancy combat practice flying they must stay inside an posted-active restricted area or warning area.(which is generally still monitored and controlled by civilian ATC)


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In what way are the airfoils used for a propeller different from the ones used in turbofan engine?
Airfoils are used in the blades of a propeller as well as the blades of the fan, axial compressor and turbine in a turbofan engine. Thus, the airfoils used in above two applications have different purposes. In propeller, the lift from the airfoil is used for generating thrust. Whereas, in a turbofan engine, airfoils are used for adding and extracting work from the flow in the compressor and turbine sections respectively. Therefore, my question is what are the characteristics of the airfoils employed in both propeller and turbofan engine, and how they vary from each other. Also, how different is the blade section of a fan with respect to the ones in axial compressor and turbine.

Note that in turbojet engine, most of the thrust is still generated by the compressor—in fact, there is more force acting on it than the total thrust, because there is negative thrust on the turbine cancelling part of it—and that a propeller also adds work (energy) to the air stream. So the principle is exactly the same in both cases. The difference is mainly in the speeds involved, the fact a compressor works against a pressure gradient, and the solidity ratio.

The angle of attack range of a propeller airfoil is larger than that of a turbofan. Therefore, the turbofan can get away with a thinner airfoil and much more camber. Also, the aspect ratio (ratio between length and chord) of a propeller blade is much higher, so the airfoil needs to be thicker to allow the blade root to carry the radial loads and to produce less torsion so the propeller blade does not twist too much under load. Were the turbofan blade as thick, the higher solidity of a typical turbofan would mean that the fan blades would block most of the flow path.


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How are jet engine RPM cycles used to monitor LCF life?
Can someone please define what are N1 and N2 throttle cycles? These are used to keep track of the accumulated low cycle fatigue (LCF) life of rotating components. But I cannot find an exact definition of them.

"N1" is the low pressure shaft speed, and "N2" is the high pressure shaft speed. N1 and N2 throttle cycles are when the throttle is moved up-down-up (or vice-a-verse), which causes the N1 and N2 speeds to go up-down-up, and hence "around" like a "cycle".
However, you will not find an "exact" definition, because it varies from engine to engine, even for the same manufacturer. In addition, the exact numbers that define the rpm changes required are usually not publicly available, as they are probably commercially sensitive.
But you can find a general description of "throttle cycles". Low cycle fatigue (LCF), is monitored by counting stress cycles. LCF is what causes a wire to break by bending it back and forth, which is a much easier way to break it, than by pulling each end. Cycling the stress back and forth (up and down) fatigues the wire and it breaks. The same thing happens in gas turbine rotating parts. As they speed up and down (in RPM) the centrifugal stresses increase and decrease. This can cause the rotating parts to fail. So they all have a "hard life", which when reached, the part is thrown away, regardless of condition.
In old engines, that don't have a monitoring system, they don't actually count each time the speed goes up and down. Instead, the engine manufacturer analyses the typical flight, and works out how many cycles occur per hour, on average. This gives an exchange ratio between hours and throttle cycles. See page4.
In modern engines, they actually count the cycles that occur. This means, if they fly the plane slightly differently than intended, the life being consumed is correctly recorded, whereas the exchange ratio would be wrong. (Though the life limit still needs to be verified as correct for the different mission profile).
Typically, 1 cycle is from idle to max speed, and back to idle. 60% to max and back to 60% may be 0.5 cycles, and 75% to max and back to 75% 0.25 cycles, as an example. So, if you take-off, from idle, do a climb at max RPM, throttle back in cruise to 60%, return to max before landing, and then shutdown the engine, you have accumulated 1+0.5+0.25=1.75 cycles in the flight. (Recognising that when you go from 60 to max back to 60, you have meet the criteria for both the 0.5 and 0.25 cycles.)
e.g. Another example of throttle cycles:


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For designing a runway, what are the largest cargo airplanes in use?
I am working on a project where I have to design a runway for large cargo planes and I need to know what kind of planes I should assume would land there.

It depends on a lot of factors, such as the number of packages to be transported, available runway length, local climate, political connection with other countries, etc.

Thank you for your answer Kevin, however i just need to know what cargo planes are most commonly used today.

If you plan around the latest variant of the 747, everything else in use will pretty well be taken care of.  UPS flies 747s, FedEx flies the MD-11, which is similar. And both fly other, smaller jets as well.

Are you asking for statistics to support one type or another? That might be hard to offer. It would be easier to give prominent examples. In my experience, I see the A300, B757, B767, and B747 in frequent use. For example, UPS operates 75 B757s, 59 B767s, 52 A300s, etc. FedEx operates 119 B757s, 68 A300s, 59 MD-11s, etc. Atlas operates 45 B747s, etc. ABX operates 37 B767s.

@andrew please specify if you mean civilian or military cargo planes.

The C5 Galaxy is a large pure cargo plane, with the nose able to swing wide open.
Image source
The Ukranians make larger cargo planes than the C-5, nicknamed the vodka burners here in Australia. Slighty larger than the C-5 is the Antonov AN124.
Image source
And the largest of them all, the B747 freighter and the Antonov AN225.
Image source
Image source
The pure cargo planes have swing noses which allows for sticking big chunks of cargo straight in. We had a look at air freighting a simulator some time ago, and a regular freighter 747 could not do it, too bulky for the side loading set-up. Only the swing nose guys could manage, requiring airport facilities that could handle oversize freight.
A comparison between sizes of 747 and An225 is found on Wikipedia:
Image source

I thought all C-5s were retired? But then again I've also heard of plans to return some of them to service...

Yeah they're C-5M Super Galaxy's now.

On the C-5, the cockpit doesn't swing open; it stays put. It's the nose of the C-5 swings open.

A bit of a Duh error, have rectified.

C-5 in picture: NOM


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What is this three-bladed vintage aircraft?
We found this poster at IKEA, EDELVIK Poster 103.776.29.

Allposters.com has another poster, which includes the same aircraft, but 2 in formation, possibly the same original photo/artist?

That is a North American T-28 Trojan, a postwar era military aircraft used for basic flight training an the Navy and Marine Corps.

They still remain popular with warbird collectors and enthusiasts.

That was the closest match I did find, but wasn't sure.  All the photos of t-28's I find have the air scoops at the 12 o'clock and 5 o'clock.  The poster is 12 and 7?

@ChadWright the image in the poster could have been mirrored. In fact the poster with 2 in formation are mirrored from each other.

@fooot, just noticed that in the second poster.  Thanks, mystery solved!

That is a fine looking aircraft!


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Why do Leading Edge Flaps (LEFs) create lift while down at slow speeds, but decrease lift while down at higher speeds?
When taking off or landing, both LEFs and trailing edge flaps (TEFs) for fighter aircraft are in the down position to provide more lift. However, when flying around at higher speeds (let's say 500-600 knots), the left LEF going down and the right LEF going up causes the aircraft to roll left.
My personal theory is that the dominant form of drag (induced) at slow speeds means that the increased camber provides more lift although slightly decreasing the angle of attack (which is good if you are close to the stall angle of the wing). However, at higher airspeeds the slight decrease in angle of attack caused by the downward LEF and also the larger parasitic drag causes the decrease in lift of the wing.
Does this theory hold up? Or is there more to it that I'm not considering?

Drag is drag, get rid of it as soon as it is not needed. Even in my 'litte' Cessna Cardinal, with 180 HP, flaps are retracted as soon the benefit of slow speed lift is overcome by sufficient lift being generated by higher climb/cruise speed. That's only 10 degrees on takeoff, just to help get over obstructions. After they are just drag.  Back down again for landing for more lift at lower speeds, all the way to 30 degrees for touchdown.

I don't know of ANY fighter aircraft with Leading-Edge Flaps. Slats yes, but not Flaps.

the left LEF going down and the right LEF going up causes the aircraft to roll left<< This NEVER happens. Leading edge devices are always moved symmetrically.

@RAC F-16, F-18, to name a couple. Perhaps I should've worded the question differently. Say, for example, the left LEF of an F-16 gets stuck in the down position... The aircraft will have a left roll tendency for the rest of flight because the left wing is now producing less lift. Why, then, do we put LEFs in the down position when coming in for a landing? Is it to increase camber to allow the aircraft to maintain the same wing angle of attack at slower speeds without stalling?

Re " However, when flying around at higher speeds (let's say 500-600 knots), the left LEF going down and the right LEF going up causes the aircraft to roll left." -- the question would benefit from an explanation of how you know this to be true.  Personal experience?  Outside sources? Not saying it's implausible, but some of us would like to know how you know this to be true.  But doesn't it make sense that at low AoA, the LE flap would just sort of act as a front-mounted aileron?

Have a look at this question. In general the wing alone is best at generating the most lift per drag, so the moment you don't need the extra lift anymore, you close all high lift devices, to maximize lift over drag.

Leading edge flaps, also known as slats, don't really create lift. The effect on lift coefficient is minor (less than 10% in general) but they help increase the stall angle of attack.
As a summary, flaps creates lift by increasing surface area and profile camber, whereas slats postpone the stall and allow for higher AOA by reducing pressure drop around the leading edge. This increases the theoretical maximal lift by increasing the stall AOA but doesn't change much the lift coefficient.
Slats are ment to work at high AOA by design, at higher speed your AOA is very small, the slat is thus not working properly, disrupting the flow on the suction side of the wind and reducing actual AOA, thus reducing lift of that particular wing while simultaneously increasing drag.

This site has some info on what the F-16 leading & trailing edges do during the flight - symetrically. We can see that at high speeds the wing is straight: it is at a low angle of attack, and at high speed the drag needs to be low.
When AoA is high, it needs the slats to be deflected, while at low speeds the flaps are deflected as well. The Approach configuration works as a thin wing with high camber.

The only reason I can think of is angle of attack. At low speed, angle of attack is higher, so even the downward drooping section ends up with a positive AoA, creating lift. At high speed, it is lower, causing the downward drooping section to have negative AoA, and thus create negative lift.
Now, why do we have this device in the first place then? (At least partly) Because a gradual curve, rather than a flat plate, results less drag and safer stall behavior.

When the leading edge flaps (slats) go down, they reduce the effective angle of attack, but allow increasing more by pitching the nose up. So

When deployed down symmetrically, the plane can fly slower by increasing the angle of attack, assuming a nose higher attitude than it would otherwise be able to sustain for the same flight path.
When deployed asymmetrically, the decrease of effective angle of attack on the side where it is down means overall lift decreases there—though the increase in camber increases the lift coefficient a bit, so the decrease is less than if the whole wing was rotated—and increases on the side where it is up—though again the negative camber reduces the lift coefficient a bit. That means it's not as efficient as using the trailing edge devices (ailerons) where the change in camber works in the same direction with the change of effective angle of attack.

The LEF's (leading edges in front of the wings) go down symmetrical,  there is a asymmetry brake system built in  to prevent that asymmetrical deflection if more than a few degrees (5 degrees) difference is sensed, immediately.  Flaps or flaperons from the behind edge of the wings do that and some jets have stabilators  moving like scissors  to do this. At slower speed the amount of angle of attack is huge and this provides lift. At high speed angle of attack is small and LEF's in down position create drag more than normal values because the airflow is tangent not in line with the  leading edges angle of deflection .

Suggestion: delete sentence "You don't roll if the LEF's are asymmetrical."  It doesn't seem to add anything, and is potentially confusing.  If the LEF's were asymmetrical, you very well might roll.

True when you roll the F-18 SuperHornet. I assume that is valid for legacy Hornet to.


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Flight Control Weight limitations
Does anybody know any limitations of flight control weights?
For instance elevators must have same weight? What is the acceptabld difference/limits and what would be the reason of overweighting? (Paint, bushings, repairs etc).
Please consider A320s and B737s for giving example

Flight control mass balance weights are used primarily to prevent things like flutter. Most airline manufacturers are able to perform analysis of their designs to determine the exact weight to introduce, and where to place it. The rest use static balancing. This article from the Experimental Aircraft Association is not an airliner example, but it provides a good explanation of the why and how of flight control balancing.

this is not what I am looking for.  aircraft maintenance manual of an A319 doesn't specify why/wether or not RH elevator should be heavier than LH elevator.

Probably because that information is only useful to depot maintenance facilities that perform work requiring r/r of flight control surfaces/


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What does "Crew: Top of your mind!" mean in commercial aircrafts?
On a flight this year in Europe, the pilot or co-pilot announced midflight "Crew: Top of your mind!" via the loudspeakers. The crew didn't visible react on that and I couldn't notify any change in the flight after that. What does this announcement mean?
The flight was either with Swiss, Air Serbia, SAS or IcelandAir. Unfortunately, I can't remember which one.

Can you remember which part of the flight this was? And I'm guessing it was in English?

It was more or less midflight and it was in English

Just a wild guess, it could have been related to a previous conversation between the captain and the flight crew, intended to remind the flight crew about something.

Despite being in English, it may come from English-as-a-second-language crew, so they could have meant something completely different (lost in translation). Whatever it was, it is not a standard call-out.

Could it rather be « crew: top of climb » which some airlines use, but 2 things contradict this: a TOC mid flight is unlikely and although used by some airlines it is more the top of descend we indicate to the flight attendants for them to start preparing for landing.

I don't think I've ever heard any variation of "top of descent" other than something very close to "cabin crew, prepare cabin for landing", but it's been a while since I flew commercially.

ToC for the last step climb?

Top of climb sounds reasonable. By mid flight I wasn't referring to the middle of the flight, but more to the normal flight instead of the start or the landing. Sorry for the confusion. But why does the pilot announce the end of the climb?

These is probably internal SOP's(Standard Operating Procedure) i.e implemented by the company itself maybe to signal the cabin crew to start a procedure(serve drink, prepare meals in the galley etc...)


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Mathematical model used in free route airspace
As a new researcher in an air traffic institute, I am currently looking into mathematical models - promising or otherwise - that are used in modelling free route airspace.
What is a good place to begin?
Thanks in advance.

Welcome to Av.SE. What exactly is “free route airspace”?

@RalphJ http://www.eurocontrol.int/articles/free-route-airspace

En-route simulation by airtopsoft is a good simulation modeling software package that I have utilized in the past to model airspace routing. It also give you some pretty powerful tools to analyze the data afterward.
Another commonly used mathematical tool for modeling airspace and routing is the "Airspace Concept Evaluation System" (ACES). This platform uses four-degrees-of-freedom equations of motion to model aircraft performance and navigation data. Based on the trajectory data, it generates "pseudo-radar" tracks to help predict collision avoidance patterns. I believe this tool is more commonly used to predict routes in the NAS but I believe you could utilize it for free route airspace by playing with the input parameters.
Hope this gives you a good place to start!


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Is there a limit to how many hours a person can fly per month?
I'm trying to figure out whether there's a maximum per person.  Of course factoring in eight hours of sleep and say maintenance time there is definitely a limit, but I don't see where it is.

Each country will have its own regulations on this, and each airline may have its own policies, so it would help if you could narrow this down at least to a country.

Welcome to aviation.SE! Are you asking what's practically possible, or what's legally allowed? If you're asking about the legal part, please tell us which country you're asking about. And we do have some relevant questions already: here, here

Are you asking about how much a pilot is allowed to fly or a person can fly as a passenger?

@ymb1 How do you know the question is about the US? Or are you just making it about the US to benefit from the answer, even if we don't know the OP's intention?

@ymb1 I think using a good answer is fine, if the OP doesn't follow up. I don't know if there's any SE etiquette that says we shouldn't.

Well, there certainly is because there are only so many hours per month.

Depending on the month, between 672 and 744 hours.

With respect to air carrier operations in the US, 14 CFR 121.481 requires:

(e) No pilot may fly as a member of a crew more than 100 hours during any one calendar month.
(f) No pilot may fly as a member of a crew more than 1,000 hours during any 12-calendar-month period.

14 CFR 135.265 commuter:

(1) 1,200 hours in any calendar year.
(2) 120 hours in any calendar month.

Under Part 91, fractional ops, 14 CFR 91.1059 states:

(a) No program manager may assign any flight crewmember, and no flight crewmember may accept an assignment, for flight time as a member of a one- or two-pilot crew if that crewmember's total flight time in all commercial flying will exceed -
(1) 500 hours in any calendar quarter;
(2) 800 hours in any two consecutive calendar quarters;
(3) 1,400 hours in any calendar year.

Otherwise, there is no direct limit under Part 91. However, if you are fatigued enough to cause a problem, FAA can still charge you under general "unsafe operation" rules.


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Why would an F16 battery make a buzzing sound?
According to this YouTube Video I heard the mechanism that moved the canopy, and then I heard a small buzzing sound. The video description says that it is spooling something, but I don't know what exactly.
Also, I am completely blind, so I have nothing to look at and only rely on sounds to know what is happening.

Are you refering to this sound? link

Yes, right after the canopy closes with a loud hissing sound, a few seconds later you hear a faint buzzing sound rising in pitch, and it happens a second time, but a little lower in pitch, though still rising.

The relevant part from the video description that you referred to:

You'll here a buzz, thats the battery, then you'll here it spooling thru N (nancy) stages.

The word "spooling" does not refer to the battery, it refers to the engine. The battery is static and does not spool.
There are several measurements or indications used to convey a turbine engine's state. One of them is N2 (others include N1, Engine Pressure Ration, Exhaust Gas Temperature, Interstage Turbine Temperature and several others).
Back to the video description. In this case I believe the author was referring to the N2 measurement that raises ("spools") and needs to be monitored during engine start.
N1 is the low-pressure compressor speed, and N2 is the engine's high-pressure compressor speed (both usually expressed in percentages rather than actual RPM).
More information about N1 and N2 can be found here: What are N1 and N2?


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Why doesn't EVA Air BR087 (Taipei to Paris) follow the shortest path?
I've noticed that the flight BR087 from TPE to CDG doesn't follow an orthodrome.
Instead, it seems to take great pains to avoid the Chinese airspace entirely.

Why? EVA Air has other flights connecting Taiwan to China.
For instance, a similar flight KLM808 follows the orthodrome more closely :

Related: https://aviation.stackexchange.com/questions/13428/why-dont-airlines-fly-a-great-circle-route-between-barcelona-and-d%c3%bcsseldorf